Issue #4085 has been updated by trans (Thomas Sawyer).
@headius Thank you. I see how matz is conceiving of refinements now. Previous explanations as a means of safe monkey patching are not really accurate. It's not monkey patching. It is more akin to a macros --macros that intercept method calls. And thus I see how it avoids violation of modularity, b/c it doesn't effect any method that is not *explicitly* invoked within the scope of `using` the refinement.
So refinements, as it turns out, are rather a weak sauce. They CANNOT be used to "safely" interject behavior into pre-existing reusable classes. So I don't expect they will have much value for general system design. Primarily refinements will be useful for things like debugging and profiling.
Can they serve as a reliable replacement for monkey patching? To the extent that it is just to *add* a behavior, as opposed to changing a pre-existing behavior, then refinements might suffice. I think it remains to be seen how well they will really workout in this regard --whether a library like Facets or ActiveSupport should switch to a refinement only design, and whether they have any good use at all beyond that.
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Feature #4085: Refinements and nested methods
https://bugs.ruby-lang.org/issues/4085#change-34330
Author: shugo (Shugo Maeda)
Status: Assigned
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: 2.0.0
=begin
As I said at RubyConf 2010, I'd like to propose a new features called
"Refinements."
Refinements are similar to Classboxes. However, Refinements doesn't
support local rebinding as mentioned later. In this sense,
Refinements might be more similar to selector namespaces, but I'm not
sure because I have never seen any implementation of selector
namespaces.
In Refinements, a Ruby module is used as a namespace (or classbox) for
class extensions. Such class extensions are called refinements. For
example, the following module refines Fixnum.
module MathN
refine Fixnum do
def /(other) quo(other) end
end
end
Module#refine(klass) takes one argument, which is a class to be
extended. Module#refine also takes a block, where additional or
overriding methods of klass can be defined. In this example, MathN
refines Fixnum so that 1 / 2 returns a rational number (1/2) instead
of an integer 0.
This refinement can be enabled by the method using.
class Foo
using MathN
def foo
p 1 / 2
end
end
f = Foo.new
f.foo #=> (1/2)
p 1 / 2
In this example, the refinement in MathN is enabled in the definition
of Foo. The effective scope of the refinement is the innermost class,
module, or method where using is called; however the refinement is not
enabled before the call of using. If there is no such class, module,
or method, then the effective scope is the file where using is called.
Note that refinements are pseudo-lexically scoped. For example,
foo.baz prints not "FooExt#bar" but "Foo#bar" in the following code:
class Foo
def bar
puts "Foo#bar"
end
def baz
bar
end
end
module FooExt
refine Foo do
def bar
puts "FooExt#bar"
end
end
end
module Quux
using FooExt
foo = Foo.new
foo.bar # => FooExt#bar
foo.baz # => Foo#bar
end
Refinements are also enabled in reopened definitions of classes using
refinements and definitions of their subclasses, so they are
*pseudo*-lexically scoped.
class Foo
using MathN
end
class Foo
# MathN is enabled in a reopened definition.
p 1 / 2 #=> (1/2)
end
class Bar < Foo
# MathN is enabled in a subclass definition.
p 1 / 2 #=> (1/2)
end
If a module or class is using refinements, they are enabled in
module_eval, class_eval, and instance_eval if the receiver is the
class or module, or an instance of the class.
module A
using MathN
end
class B
using MathN
end
MathN.module_eval do
p 1 / 2 #=> (1/2)
end
A.module_eval do
p 1 / 2 #=> (1/2)
end
B.class_eval do
p 1 / 2 #=> (1/2)
end
B.new.instance_eval do
p 1 / 2 #=> (1/2)
end
Besides refinements, I'd like to propose new behavior of nested methods.
Currently, the scope of a nested method is not closed in the outer method.
def foo
def bar
puts "bar"
end
bar
end
foo #=> bar
bar #=> bar
In Ruby, there are no functions, but only methods. So there are no
right places where nested methods are defined. However, if
refinements are introduced, a refinement enabled only in the outer
method would be the right place. For example, the above code is
almost equivalent to the following code:
def foo
klass = self.class
m = Module.new {
refine klass do
def bar
puts "bar"
end
end
}
using m
bar
end
foo #=> bar
bar #=> NoMethodError
The attached patch is based on SVN trunk r29837.
=end
--
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